1. Field of the Invention
The present invention relates to a cutting insert which is used in turning operations of work materials for grooving, cutting-off, or the like.
Priority is claimed on Japanese Patent Application No. 2007-091952, filed Mar. 30, 2007, Japanese Patent Application No. 2007-094884, filed Mar. 30, 2007, and No. 2008-012974, filed Jan. 23, 2008, the contents of which are incorporated herein by reference.
2. Description of Related Art
A cutting insert for grooving, cutting-off or the like used in a turning operations is proposed, for example, in Japanese Unexamined Patent Application, First Publication No. H09-174308 (hereinafter, JP H09-174308), so as to have a pair of ridges extending substantially in a longitudinal direction on a top surface of a cutting head, a chip breaker pit which is provided between the ridges, a break line extending between a front pit and a rear pit of the chip breaker pit, and a pair of burls included and disposed in the front pit between the break line and a major cutting edge, so that the vicinity of a connecting point of the break line with the ridges thrust chips as a squeezing zone.
In the cutting insert of JP H09-174308, the pair of burls is disposed in the vicinity of inner surfaces of the ridges facing each other. Each of the ridges extends in the longitudinal direction and toward a corner portion in which a front major cutting edge (i.e. a front cutting edge) meets a side cutting edge so that the front end thereof is separated from that of the other ridge.
However, in the cutting insert of JP H09-174308, when grooving a work material by advancing the front major cutting edge in the longitudinal direction and broadening the groove width using the side cutting edge feeding in a traverse direction, whole chips generated by the side cutting edge especially at the vicinity of the corner portion are collided with the front ends stretching from the ridges. Therefore, in such a case, it is possible to increase the cutting resistance and impossible to dispose the chips smoothly owing to an accumulation of the chips.
In such grooving and cutting-off of the work material, cutting fluid (i.e. coolant) is generally supplied to a cutting portion in which a cutting edge cuts deep into the work material for lubrication and cooling. The cutting fluid is supplied toward a top surface, i.e. a rake face, of the cutting head from the rear end of the cutting insert in order to not be prevented by the chips from being supplied.
However, in the cutting insert of JP H09-174308, the ridges are formed so as to extend in the longitudinal direction so that the front ends thereof extend toward the corner portions. Therefore, the cutting fluid which is supplied to the front ends running between the ridges and the side cutting edges in the rake face is guided by the front ends of the ridges. As a result, the cutting fluid cannot be sufficiently supplied to the front major cutting edge, especially at the corner portion; therefore, damage by heat of the cutting edge at the corner portion and adhesion depending on the work material can easily occur. In addition, walls of the groove and the cut surfaces of the work material are deteriorated in accuracy and quality.
Meanwhile, when only grooving or cutting-off the work material at the front major cutting edge by advancing the cutting insert in the longitudinal direction, the chips generated by the front major cutting edge collide with and rub against the pair of burls, and move to the chip breaker pit. The burls (bosses) are worn and the height thereof becomes low, thereby disappearing if the chips continue rubbing. The tool life of the cutting insert is wasted in a short amount of time since the chips cannot be controlled owing to the abrasion of the burls; also, smooth operation is impossible since the chips cannot be controlled during a reducing process of the burls by the abrasion.